Optical sensor configuration for ratiometric correction of blood glucose measurement

ABSTRACT

Embodiments of the invention are directed to an optical sensor for detecting blood glucose. The sensor comprises a chemical indicator system disposed within a gap between the distal end of an optical fiber and an atraumatic tip portion, wherein the optical fiber and atraumatic tip portion are coupled by a coupling member, such as a rod or hypotube or cage that traverses the gap. The sensor further comprises a means for generating and detecting an optical reference signal unrelated to the blood glucose, such that ratiometric correction of blood glucose measurements for artifacts in the optical system is enabled.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the invention are directed to an optical sensor fordetecting an analyte, preferably glucose. In preferred embodiments, thesensor comprises an optical fiber having a fluorescence chemistrydisposed along the distal region of the fiber, more preferably locatedbetween the distal end of the fiber and an atraumatic tip.

2. Description of the Related Art

Hyperglycemia and insulin resistance are common in critically illpatients, even if such patients have not previously had diabetes. Inthese situations, glucose levels rise in critically ill patients therebyincreasing the risk of damage to a patient's organs. Further, studieshave shown that normalization of blood glucose levels with insulintherapy improves the prognosis for such patients, thereby decreasingmortality rates.

More recent scientific evidence confirms that dramatic improvements inthe clinical outcome of hospitalized Intensive Care Unit (ICU) patientscan result from tight therapeutic control of blood glucose to normalranges. These studies indicate that Tight Glycemic Control (TGC) of ICUpatients may reduce mortality by as much as 40%, and significantly lowercomplication rates. In these situations, it is necessary to accurately,conveniently and continuously monitor blood sugar in a real-time devicespecifically designed to meet the challenging needs of the ICUenvironment. Researchers at Johns Hopkins University estimate that TGCcan save as many as 150,000 lives and reduce U.S. healthcare costs by asmuch as $18 billion annually.

Performing TGC requires continuous and accurate monitoring of apatient's blood glucose levels. Thus, there is a need for a real-timeglucose monitoring system that is adapted to meet the needs of ICUpatients.

SUMMARY OF THE INVENTION

A sensor for detecting an analyte concentration in a blood vessel isdisclosed in accordance with an embodiment of the invention. The sensorcomprises: an optical fiber with proximal and distal ends; an atraumatictip portion with proximal and distal ends, wherein the proximal end ofthe atraumatic tip portion is separated from the distal end of theoptical fiber, such that a gap exists between the atraumatic tip portionand the optical fiber; a rod with proximal and distal ends, wherein theproximal end of the rod is attached to the distal end of the opticalfiber, and wherein the distal end of the rod is attached to the proximalend of the atraumatic tip portion, such that the rod traverses the gapand couples the optical fiber to the atraumatic tip portion; a chemicalindicator system capable of generating an emission light signal inresponse to an excitation light signal, wherein the intensity of theemission light signal is related to the analyte concentration, andwherein the chemical indicator system is disposed within the gap; and aselectively permeable membrane disposed over the gap, wherein the sensoris sized for deployment within the blood vessel.

In one variation to the analyte sensor, the chemical indicator system isimmobilized within the gap by a hydrogel. In another variation, thesensor further comprises a temperature sensor. The optical fiberpreferably has a diameter of between about 0.005 inches and about 0.020inches. In another variation, the sensor further comprises a reflectiveregion. Preferably, the reflective region comprises a reflective surfaceof the proximal end of the rod. In one embodiment, the rod may beattached to the optical fiber and atraumatic tip portion by heating. Inanother embodiment, the rod may be attached to the optical fiber by areflective or optically clear adhesive.

In variations to the sensor, the shape of the distal end of theatraumatic tip portion may be configured to reduce trauma within theblood vessel. In various embodiments, the shape of the distal end of theatraumatic tip portion may be selected from the group consisting ofhemispherical, parabolic, and elliptical. In another variation, thedistal end of the atraumatic tip portion is flexible. In anothervariation, the distal end of the atraumatic tip portion is deformable.The distal end of the atraumatic tip portion may be formed from at leastone material selected from the group consisting of plastics, polymers,gels, metals and composites.

The rod may be formed from at least one material selected from the groupconsisting of metal, metal alloy, plastic, polymer, ceramic, andcomposite material. In a preferred variation, the rod is formed fromstainless steel, titanium, or Nitinol. In one embodiment, the rod iscylindrical. Preferably, the rod diameter is between about 0.002 inchesand about 0.010 inches. The rod may be flexible in some embodiments. Therod is stiffer than the optical fiber in some embodiments. In suchembodiments, the rod is preferably sufficiently stiff to prevent flexingof the sensor along the gap.

A sensor for detecting an analyte concentration in a blood vessel isdisclosed in accordance with another embodiment of the presentinvention. The sensor comprises: an optical fiber with proximal anddistal ends; an atraumatic tip portion with proximal and distal ends,wherein the proximal end of the atraumatic tip portion is separated fromthe distal end of the optical fiber, such that a gap exists between theatraumatic tip portion and the optical fiber; a hypotube with proximaland distal ends, wherein the proximal end of the hypotube is attached tothe distal end of the optical fiber, and wherein the distal end of thehypotube is attached to the proximal end of the atraumatic tip portion,such that the hypotube traverses the gap and couples the optical fiberto the atraumatic tip portion, wherein the hypotube comprises at leastone window that opens onto the gap; a chemical indicator system capableof generating an emission light signal in response to an excitationlight signal, wherein the intensity of the emission light signal isrelated to the analyte concentration, and wherein the chemical indicatorsystem is disposed within the gap; and a selectively permeable membranedisposed over the at least one window, wherein the sensor is sized fordeployment within the blood vessel. In preferred embodiments, thechemical indicator system is immobilized by a hydrogel within the cavityformed within the hypotube. In further preferred embodiments of thesensor with hypotube, a reflective member is disposed within the sensor.In further preferred embodiments of the sensor with hypotube, afluorescent member is disposed within the sensor.

A sensor for detecting an analyte concentration in a blood vessel isdisclosed according to another embodiment of the present invention. Thesensor comprises: an optical fiber with proximal and distal ends; anatraumatic tip portion with proximal and distal ends, wherein theproximal end of the atraumatic tip portion is separated from the distalend of the optical fiber, such that a gap exists between the atraumatictip portion and the optical fiber; a cage connecting the optical fiberand atraumatic tip portion, wherein the optical fiber is at leastpartially enclosed within the cage, and wherein the cage has at leastone window; a chemical indicator system disposed within the cage,wherein the chemical indicator system is adjacent the window and isseparated from analyte by a selectively permeable membrane, and whereinthe chemical indicator system is capable of generating an emission lightsignal in response to an excitation light signal, wherein the intensityof the emission light signal is related to the analyte concentration;and a reference material, wherein the reference material is configuredto either reflect a portion of the excitation light signal before theexcitation light signal enters the chemical indicator system or toreturn a second emission light signal, wherein the intensity of thesecond emission light signal is not related to the analyteconcentration.

In another embodiment, a method for measuring glucose concentration isprovided. The method comprises transmitting a first light in a firstdirection through an optical fiber to a glucose sensor, where theglucose sensor comprises a hydrogel cavity having a fluorophore system.At least a portion of the first light is reflected off a reflectivesurface of the glucose sensor as a second light in a second directionopposite the first direction. A third light is emitted in the seconddirection. The third light results from the chemical indicator systemfluorescing. The method further comprises calculating the glucoseconcentration, where the glucose concentration is determined by theratio of the emitted third light to the reflected second light. Theratio is independent of the intensity of the first light.

In another embodiment, a method for measuring glucose concentration isprovided. The method comprises transmitting a first light in a firstdirection through an optical fiber to a glucose sensor, where theglucose sensor comprises a hydrogel cavity having a fluorophore systemwhich is sensitive to glucose as well as a second fluorophore which isglucose insensitive. A second light from the glucose sensitivefluorophore is emitted in a second direction opposite the firstdirection. A third light from the glucose insensitive fluorophore isalso emitted in the second direction. The method further comprisescalculating the glucose concentration, where the glucose concentrationis determined by the ratio of the emitted second light to the emittedthird light. The ratio is independent of the intensity of the firstlight.

In another embodiment, a system for measuring glucose is provided. Thesystem comprises at least one light source, at least one optical fibercoupled to the light source, any one of the glucose sensors describedabove coupled to the optical fiber, and a data processing device coupledto the glucose sensor.

In another embodiment, a method for manufacturing a glucose sensor isprovided. The method comprises inserting a first end of a rod into anoptical fiber, inserting a second end of the rod into an atraumatic tip,surrounding the rod with a hydrogel cavity, and enclosing the hydrogelcavity with a selectively permeable membrane.

In another embodiment, a method for manufacturing a glucose sensor isprovided. The method comprises cutting a window in a hypotube,contacting an optical fiber with a first end of the hypotube, andheating the optical fiber, such that the optical fiber swells to fullycontact the first end of the rod.

In another embodiment, a sensor for detecting an analyte concentrationin a blood vessel is provided. The sensor comprises an optical fiberwith a proximal end and a distal end. The distal end of the opticalfiber comprises a glucose sensing hydrogel. The glucose sensing hydrogelcomprises a first fluorophore, a quencher, and at least one glucosereceptor. A reference fiber is adjacent the optical fiber and has aproximal end and a distal end. The distal end of the reference fibercomprises a reference material. The reference material comprises asecond fluorophore. A light emitting diode is operably coupled to theglucose fiber and the reference fiber. The light emitting diode sends anexcitation light to the glucose fiber and the reference fiber. A glucosesignal detector is operatively coupled to the glucose fiber. The glucosesignal detector receives a first fluorescent light from the glucosefiber. A reference signal detector is operatively coupled to thereference fiber. The reference signal detector receives a secondfluorescent light from the reference fiber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a glucose sensor having a series of holes that form ahelical configuration.

FIG. 1B shows a glucose sensor having a series of holes drilled orformed at an angle.

FIG. 1C shows a glucose sensor having at least one spiral groove.

FIG. 1D shows a glucose sensor having a series of triangular wedgecut-outs.

FIG. 2A shows a cross-sectional view of one embodiment of a glucosesensor having a cavity in the distal portion of the sensor and atemperature probe.

FIG. 2B shows a perspective view of the glucose sensor shown in FIG. 2.

FIG. 3A shows a cross-sectional view of another embodiment of a glucosesensor having a cavity in the distal portion of the sensor.

FIG. 3B shows a perspective view of the glucose sensor shown in FIG. 4.

FIG. 4 shows a cross-sectional view of another embodiment of a glucosesensor having a window opening to a cavity in the distal portion of thesensor.

FIG. 5 shows a cross-sectional view of another embodiment of a glucosesensor having a cavity in a distal portion of the sensor enclosed withina cage and an additional reference material.

FIG. 6 shows a cross-sectional view of another embodiment of a glucosesensor having a cavity in a distal portion of the sensor and anadditional reference material.

FIG. 7 shows a cross-sectional view of another embodiment of a glucosesensor having a cavity in a distal portion of the sensor enclosed withina cage and a reference material extending to the atraumatic tip.

FIG. 8 shows a cross-sectional view of another embodiment of a glucosesensor having a cavity in a distal portion of the sensor enclosed withina cage and a reference material as a bar extending across the diameterof the cage.

FIG. 9 shows a cross-sectional view of another embodiment of a glucosesensor having a cavity in a distal portion of the sensor enclosed withina reference material, further enclosed within a cage.

FIG. 10 shows a cross-sectional view of another embodiment of a glucosesensor having a cavity in the distal portion of the sensor enclosedwithin a cage and a reference material as a bar embedded within theoptical fiber.

FIG. 11 shows a cross-sectional view of another embodiment of a glucosesensor having a cavity and a reference material side-by-side in thedistal portion of the sensor enclosed within a cage.

FIG. 12 shows a cross-sectional view of another embodiment of a glucosesensor having a cavity in the distal portion of the sensor enclosedwithin a cage and a translucent reference material between the opticalfiber and cavity.

FIG. 13 shows a schematic view of another embodiment of a glucose sensorhaving a glucose sensing optical fiber adjacent to a reference opticalfiber.

FIG. 14 shows a glucose measurement system comprising one excitationlight source, a single exciter-dual emitter fluorophore system, and amicrospectrometer and/or spectrometer.

FIG. 15 shows the Stern-Volmer quenching of HPTS-CysMA/3,3′-oBBV insolution.

FIG. 16 shows the glucose response of HPTS-CysMA/3,3′-oBBV in solution.

FIG. 17 shows the glucose response of HPTS-CysMA/3,3′-oBBV in hydrogel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Various embodiments of optical systems and methods are disclosed hereinfor determining blood glucose concentrations. The various embodimentspreferably share at least two features. First, they involve exciting achemical indicator system with an excitation light signal and measuringthe emission light signal of the indicator system, wherein the indicatorsystem is in contact with the blood and comprises a fluorescent dyeoperably coupled to a glucose binding moiety-such that the emissionlight signal generated by the indicator system upon excitation isrelated to the blood glucose concentration. Second, they involvecorrecting the blood glucose concentration measurements from theindicator system for potential artifacts due to the optical system,which artifacts are unrelated to the blood glucose concentration. Thecorrection is performed by ratiometric analysis. More particularly, theratio of emission light signal to a second light signal that ispropagated through the optical system, e.g., the excitation light signalor a separate reference light signal, is used for correcting anynon-glucose related contributions of the optical system. Where theexcitation light signal is used for the ratiometric correction, thesensor preferably includes a reflective surface, e.g., a minor, locatedsomewhere along the sensor, such that at least a portion of theexcitation light which has passed through the optical system isreflected back to a detector. Where a separate reference light signal isused, the reference light signal may either be: (1) generated by aseparate light source and reflected back to a detector, or (2) generatedas a separate emission light signal from a separate dye disposedsomewhere along the sensor. Thus, a glucose sensor in accordance withpreferred embodiments of the present invention will comprise either areflective surface or a second dye adapted to emit a reference lightsignal.

Various structural configurations have been proposed for holding achemical indicator system in a position, which is: (1) exposed to theblood, (2) disposed within the excitation light path, and (3) forexposing a chemical indicator system to the blood and, for introducingto the indicator system an excitation light signal, for detecting anemission light signal from the indicator system, and for enablingratiometric correction of glucose determinations for artifacts of thesystem optics; see in particular 2008/0188725. More particularly,aspects of the present invention relate to improvements and alternativeembodiments for generating a reference light signal (as discussed in2008/0188725), either through various mirror/reflective surfaceconfigurations adapted to return a portion of the excitation lightsignal back to a detector or through generating a separate emissionlight signal from a separate dye. Aspects of the present inventionrelate to new and improved configurations for disposing a chemicalindicator system within an interrogation light path, wherein the sensoris more robust and exhibits improved patient tolerance.

Optical glucose sensors, such as those described in U.S. Patent Publ.Nos. 2008/0188722, 2008/0188725, 2008/0187655, 2008/0305009,2009/0018426, 2009/0018418, and co-pending U.S. patent application Ser.Nos. 11/296,898, 12/187,248, 12/172,059, 12/274,617 and 12/424,902 (eachof which is incorporated herein in its entirety by reference thereto)typically employ a chemical indicator system disposed at the distal endof an optical fiber, wherein the indicator system is maintained incontact with the blood, such that an excitation light signal sentdistally down the fiber causes the chemical indicator system to emit alight signal related to the concentration of glucose.

In certain embodiments, an optical glucose measurement system isdisclosed for measuring glucose concentration in blood using one or moreglucose-sensing chemical indicator systems. Such indicator systemspreferably comprise a fluorophore operably coupled to a glucose bindingmoiety. Preferably, the glucose binding moiety acts as a quencher withrespect to the fluorophore (e.g., suppresses the fluorescent emissionsignal of the fluorophore in response to excitation light when itassociates with the fluorophore). In preferred embodiments, as theglucose binding moiety binds glucose (e.g., as glucose concentrationsrise), it dissociates from the fluorophore, which then generates afluorescent emission signal upon excitation. Accordingly, in suchembodiments, the higher the glucose concentration, the more glucosebound by the binding moiety, the less quenching, and the higher thefluorescence intensity of the fluorophore upon excitation.

In certain embodiments, the optical glucose measurement system measuresglucose concentrations intravascularly and in real-time through the useof such chemical indicator systems. In certain embodiments, theglucose-sensing chemical indicator systems are immobilized in ahydrogel. The hydrogel may be inserted into an optical fiber such thatlight may be transmitted through the hydrogel while at least a portionof the hydrogel is in contact with blood. The hydrogel is preferablypermeable to blood and analytes, specifically glucose. In certainembodiments, the optical fiber together with the hydrogel comprises aglucose sensor that is placed in a mammalian (human or animal) bloodvessel.

Examples of glucose-sensing chemical indicator systems and glucosesensor configurations for intravascular glucose monitoring include theoptical sensors disclosed in U.S. Pat. Nos. 5,137,033, 5,512,246,5,503,770, 6,627,177, 7,417,164 and 7,470,420, and U.S. Patent Publ.Nos. 2008/0188722, 2008/0188725, 2008/0187655, 2008/0305009,2009/0018426, 2009/0018418, and co-pending U.S. patent application Ser.Nos. 11/296,898, 12/187,248, 12/172,059, 12/274,617 and 12/424,902; eachof which is incorporated herein in its entirety by reference thereto.

Light may be transmitted into an optical glucose sensor from a lightsource. In certain embodiments, the light source is a light emittingdiode that emits an optical excitation signal. The optical excitationsignal excites the fluorophore system(s), such that the fluorophoresemit light at an emission wavelength. In certain embodiments, thefluorophore systems are configured to emit an optical emission signal ata first wavelength having an intensity related to the blood glucoseconcentration in the blood vessel. In certain embodiments, light isdirected out of the glucose sensor such that the light is detected by atleast one detector. The at least one detector preferably measures theintensity of the optical emission signal, which is related to theglucose concentration present in the blood. Various opticalconfigurations for interrogating glucose-sensing chemical indicatorsystems with one or more excitation light signals and for detecting oneor more emission light signals from the chemical indicator systems maybe employed, see e.g., U.S. Patent Appl No. 12/027,158 (published as2008/0188725); incorporated herein in its entirety by reference thereto.

Glucose Activity and Tight Glycemic Control

While clinicians have used insulin for decades to regulate glucoselevels in diabetics and critically ill patients, determining precisedosages remains a problem. Insulin reduces circulating glucose levelsthrough a series of complex interactions involving a number of hormonesand cell types. Dosage protocols for insulin attempt to replicate thephysiologic secretion of the hormone by the pancreas. However,administering according to fixed times and algorithms based on bloodglucose measurements can only crudely approximate the ability of ahealthy individual to continuously adjust insulin production in responseto the amount of bioavailable glucose and the needs of the body. Thus,to determine the precise amount of insulin that should be administeredto maintain a patient's blood glucose at an appropriate level, it isnecessary to have near real-time, accurate measurements of the amount ofbioavailable glucose circulating in blood.

Unfortunately, most existing methods for determining blood glucoseconcentrations fail to provide near real-time, accurate measurements ofthe amount of bioavailable glucose. Clinicians and diabetic patientstypically rely on point-of-care testing that seems to measure glucoseconcentration in plasma, e.g., using glucometers to read test stripsthat filter separate plasma from cells in a drop of whole blood. Whilethe results can be available quickly, they vary depending on thepatient's hematocrit, plasma protein and lipid profiles, etc., and canoften be falsely elevated (See e.g., Chakravarthy et al., 2005 “Glucosedetermination from different vascular compartments by point-of-caretesting in critically ill patients” Chest 128(4) October, 2005Supplement: 220S-221S). More accurate determinations can be obtained byfirst separating the cellular components of whole blood. However, thisrequires separation of the plasma from the cellular components of blood,e.g., by centrifugation. Subsequently, isolated plasma must be storedand/or transported and/or diluted prior to analysis. Storage andprocessing conditions, e.g., temperature, dilution, etc., will almostcertainly perturb the in vivo equilibrium between the bound and free(bioavailable) glucose. Consequently, regardless of the technologysubsequently employed for measuring plasma glucose concentration (e.g.,glucose oxidase, mass spectrometry, etc.), the measured glucoseconcentration is likely no longer reflective of the amount ofbioavailable glucose in vivo. Therefore, it is not feasible to useplasma glucose measurements for near real-time monitoring and adjustmentof a patient's glucose level.

Accordingly, in certain embodiments, the preferred glucose sensorsdescribed herein measure glucose “activity” as opposed to glucoseconcentration. More precisely, glucose activity refers to the amount offree glucose per kilogram of water. In some embodiments, glucoseactivity can be measured directly using glucose sensors, such as theequilibrium, non-consuming optical glucose measurement systems discussedabove, which employ a chemical indicator system to quantify the amountof free, bioavailable glucose, which is in equilibrium between the watercompartment of blood (i.e., not associated with cells, proteins orlipids, etc.) and the glucose binding moiety/quencher. The discussion ofthe sensors that follow will often refer to the physical quantity to bemeasured as an “analyte concentration”, “glucose concentration” orsimply a “concentration.” However, it is to be understood that“concentration” as used herein, refers to both “analyte concentration”as that phrase would be ordinarily used and also to “activity” (in somecases “glucose activity”) as that phrase is described above.

Optical Glucose Sensor Configurations

With reference to FIGS. 1A-D, certain prior art embodiments (see USPatent Publication No. 2008/0188725) are illustrated. The glucose sensor117 in FIG. 1A is an optical fiber with a series holes 116 drilledstraight through the sides of the optical fiber. In certain embodiments,the holes 116 are filled with one or more glucose-sensing chemicalindicator systems. These holes may be covered with a selectivelypermeable membrane, wherein the permeability is selected such that themolecules of the chemical indicator system (e.g., fluorophore andquencher) are retained within the cavities, whereas glucose is freelypermeable. In certain embodiments, the series of holes 116 that aredrilled through the glucose sensor 117 are evenly spaced horizontallyand evenly rotated around the sides of the glucose sensor 117 to form aspiral or helical configuration. In certain embodiments, the series ofholes are drilled through the diameter of the glucose sensor.

With reference to FIG. 1B, in certain embodiments, the glucose sensor117 is a solid optical fiber with a series of holes 116 drilled throughthe sides of the fiber at an angle. In certain embodiments, the seriesof holes drilled at an angle, which are filled with hydrogel/chemicalindicator system, are evenly spaced horizontally and evenly rotatedaround the sides the glucose sensor 117. With reference to FIG. 1C, incertain embodiments, the optical fiber comprises a groove 116 along thelength of the optical fiber, wherein the groove is filled withhydrogel/chemical indicator system. In certain embodiments, the depth ofthe groove extends to the center of the optical fiber. In certainembodiments, the groove spirals around the optical fiber. In certainembodiments, the groove spirals around the optical fiber to complete atleast one rotation. In certain embodiments, the groove spirals aroundthe optical fiber to complete multiple rotations around the opticalfiber.

With reference to FIG. 1D, in certain embodiments, the glucose sensor117 is a solid optical fiber with triangular wedges 116 cut from thefiber. In certain embodiments, the triangular wedge areas are filledwith hydrogel/chemical indicator system. In certain embodiments, thetriangular wedges cut-outs are evenly spaced horizontally and around thesides of the glucose sensor 117. In certain embodiments, all lighttraveling in the glucose sensor 117 is transmitted through at least onehole or groove 116 filled with hydrogel/chemical indicator system.

In certain embodiments, as illustrated in FIGS. 2-6, the glucose sensor117 comprises an optical fiber 130 having a distal end 132, anatraumatic tip portion 134 having a proximal end 136 and a distal end138, a void or cavity 116 between the distal end 132 of the opticalfiber 130 and the proximal end 136 of the atraumatic tip portion 134,and a rod 140 connecting the distal end 132 of the optical fiber 130 tothe proximal end 136 of the atraumatic tip portion 134, wherein the rodtraverses the void or cavity. In preferred embodiments, molecules of achemical indicator system are disposed within the void or cavity 116 andimmobilized (by covalent bonding or non-covalent interaction) orotherwise associated within hydrogel matrices. See e.g., the chemicalindicator systems disclosed in U.S. Pat. Nos. 7,417,164 and 7,470,420.The cavity 116 may be loaded with hydrogel/chemical indicator system byany methods known in the art. In preferred embodiments, the cavity 116is filled with hydrogel/chemical indicator system in a liquid state. Thehydrogel/chemical indicator systems are preferably polymerized in situ,as detailed in co-pending U.S. patent application Ser. No. 12/026,396(published as 2008/0187655).

In certain embodiments, the rod 140 is attached to the optical fiber 130and/or atraumatic tip 134 by heating and expanding the optical fiber 130and atraumatic tip 134 and embedding the rod 140 there between. Incertain embodiments, the optical fiber 130 is heated to between about100° C. and about 160° C., more preferably between about 110° C. andabout 140° C. In other embodiments, the optical fiber 130 is firstheated and then cooled one or more times. In certain embodiments, therod 140 is attached to the optical fiber 130 and/or the atraumatic tip134 by applying an adhesive. In preferred embodiments, the adhesive isbiocompatible, such as for example, cyanoacrylates, epoxies, light cureadhesives, silicones, and urethanes. In certain embodiments, afterapplying the adhesive and joining the rod 140 with the optical fiber 130and atraumatic tip 134, the adhesive is cured at room temperature, byheating, or by applying UV/visible light. In certain embodiments, thetime to fix the rod 140 to the optical fiber 130 and/or atraumatic tip134 can vary from about 5 seconds to about 60 seconds, from about 15minutes to about 5 hours, from about 60 seconds to about 10 minutes, orup to about 24 hours.

In some embodiments, the proximal surface of the rod 144 is reflectiveso that a portion of the excitation light signal (or reference lightsignal) is reflected proximally down the optical fiber 130 to a detector(not shown). The term rod is used herein to refer to any elongatestructural member, regardless of its geometry, configured to connect theatraumatic tip portion to the optical fiber. The rod may be centeredcoaxially (as illustrated) or off-centered with regard to thecross-section of the fiber and atraumatic tip portion. In someembodiments, there may be more than one rod extending between the fiberand the atraumatic tip portion. Where more than one rod is employed, therods may be arranged symmetrically or asymmetrically with respect to thecross-section of the fiber and atraumatic tip portion.

In certain embodiments, as illustrated in FIGS. 5 and 6, a referencematerial 190 may be attached to the proximal surface of the rod 144. Thereference material 190 may be reflective (e.g., a minor) and functionssimilar to embodiments in which the proximal surface of the rod 144reflects at least a portion of the excitation light signal (or referencelight signal) down the optical fiber 130 to a detector (not shown). Inother embodiments, the reference material 190 comprises a separate dyeindicator system, such as for example a glucose-insensitive fluorescentdye. The excitation light from the optical fiber 130 causes theglucose-insensitive fluorophore to emit a fluorescent light back to adetector (not shown) in order to reference the emission signal from thehydrogel/chemical indicator system. In certain embodiments, the separatedye indicator system is formed of a plastic material, such as forexample polycarbonate, polyethylene, or polystyrene, infused with afluorescent dye configured to emit a separate glucose-insensitivesignal.

The hydrogel and glucose-sensing chemical indicator system is disposedwithin the cavity 116. In preferred embodiments, the hydrogel/chemicalindicator system filled cavity 116 is covered by a selectively permeablemembrane 142 that allows passage of glucose into and out of thehydrogel/chemical indicator system. Although these embodiments aredescribed using a glucose sensor 117, it should be understood by aperson of ordinary skill in the art that the sensor 117 can be modifiedto measure other analytes by changing, for example, the sensingchemistry, and if necessary, the selectively permeable membrane 142.

In certain embodiments, the selectively permeable membrane 142 isattached to the optical fiber 130 and the atraumatic tip 134 by means ofan adhesive. In preferred embodiments, the adhesive is biocompatible,such as for example, cyanoacrylates, epoxies, light cure adhesives,silicones, and urethanes. In certain embodiments, after applying theadhesive and attaching the selectively permeable membrane 142 to theoptical fiber 130 and atraumatic tip 134, the adhesive is cured at roomtemperature, by heating, or by applying UV/visible light. In certainembodiments, the time to adhere the selectively permeable membrane 142to the optical fiber 130 and/or atraumatic tip 134 can vary from about 5seconds to about 60 seconds, from about 15 minutes to about 5 hours,from about 60 seconds to about 10 minutes, or up to about 24 hours. Inother embodiments, the selectively permeable membrane 142 ispre-fabricated as a sleeve. The sleeve may be slid into place and sealedusing an adhesive and/or heated to form-fit the glucose sensor 117. Incertain embodiments, the selectively permeable membrane 142 surroundsthe entire circumference of the glucose sensor 117. In otherembodiments, the selectively permeable membrane 142 covers a window 180or opening in the glucose sensor 117 exposing the void or cavity 116 toanalytes in the blood stream.

In some embodiments, as illustrated in FIGS. 2A and 2B, the sensor 117comprises a distal portion and a proximal portion. The distal portion ofthe sensor 117 comprises the atraumatic tip portion 134, thehydrogel/chemical indicator system filled cavity 116, the rod 140, atleast the portion of the selectively permeable membrane 142 that coversthe cavity 116 and the distal end 132 of the optical fiber 130. Theproximal portion of the sensor 117 comprises the proximal portion of theoptical fiber 130. In some embodiments, the diameter, D1, of the distalportion of the sensor 117 is greater than the diameter, D2, of theproximal portion of the sensor 117. For example, the diameter D1 of thedistal portion of the sensor 117 can be between about 0.0080 inches and0.020 inches, while the diameter D2 of the proximal portion of thesensor 117 can be between about 0.005 inches to 0.015 inches. In someembodiments, the diameter D1 of the distal portion of the sensor 117 isabout 0.012 inches, while the diameter D2 of the proximal portion of thesensor 117 is about 0.010 inches.

In some embodiments, the sensor 117, including the selectively permeablemembrane 142, has a smooth surface. The smooth surface can be made forexample by the method disclosed in co-pending U.S. patent applicationSer. No. 12/026,396 (published as 2008/0187655). In summary, onepreferred embodiment of the method comprises filling the cavity 116 witha solution comprising a monomer, crosslinker and an initiator, such as athermal initiator. After the sensor 117 has been filled, the sensor 117is dipped into liquid wax, which is allowed to harden around the sensor117 and selectively permeable membrane 142.

The liquid wax has a melting point that is greater than the thermalinitiation temperature. Therefore, in order to reduce the likelihood ofinitiation during the wax dipping and coating step, the filled sensor117 can be chilled before the wax dipping and coating step. After thesensor 117 has been coated with wax, the solution in the cavity 116 canbe deoxygenated by placing the sensor 117 in a water bath while bubblingan inert gas, such as nitrogen, in the bath.

After deoxygenation, polymerization can be initiated by heating thesensor 117 to a temperature above the thermal initiation temperature,but below the melting point of the wax. Once the solution issubstantially polymerized into the hydrogel, the wax can be removed fromthe sensor by use of a solvent, such as hexane, leaving a sensor 117with a smooth surface.

In some embodiments, as illustrated in FIGS. 3A and 3B, the sensor 117comprises a distal portion and a proximal portion with substantially thesame diameter. In some embodiments, the diameter of the sensor 117 isbetween about 0.005 inches and 0.020 inches. In other embodiments, thediameter of the sensor 117 is between about 0.008 inches and 0.014inches. In other embodiments, the diameter of the sensor 117 is about0.010 inches or about 0.012 inches.

In some embodiments, the rod 140 has a proximal portion that isconnected to the distal portion of the optical fiber 130 and a distalportion that is connected to the proximal portion of the atraumatic tipportion 134. The rod 140 can be made of a metal, metal alloy, plastic,polymer, ceramic, composite material or any other material with suitablemechanical properties for connecting the atraumatic tip portion 134 withthe distal portion of the optical fiber 130. For example, the rod 140can be made of stainless steel, titanium or Nitinol. The rod 140 can becylindrical or noncylindrical, such as a bar with a square, rectangular,oval or oblong cross-section. In some embodiments, the diameter of therod 140 is generally between about 0.001 to 0.010 inches. In otherembodiments, the diameter of the rod 140 is generally between about0.004 to 0.008 inches. In other embodiments, the diameter of the rod 140is about 0.001 inches, about 0.002 inches or 0.004 inches. In someembodiments, the diameter of the rod 140 may be less than about 0.001inches. In some embodiments, the diameter of the rod 140 may be greaterthan about 0.010 inches. In some embodiments, the length of the rod 140is generally less than about 0.005 inches. In some embodiments, thelength of the rod 140 is between about 0.005 to 0.040 inches. In otherembodiments, the length of the rod 140 is generally between about 0.020to 0.040 inches. In other embodiments, the length of the rod 140 isgenerally about 0.015 inches. In some embodiments, the length of the rod140 is generally greater than about 0.005 inches.

The rod 140 adds mechanical stability to the distal portion of thesensor 117. In some embodiments, the rod 140 also adds flexibility tothe distal portion of the sensor 117, allowing the atraumatic tipportion 134 to flex back and forth relative to the orientation of theoptical fiber 130. The flexibility of the rod 140, and thus the degreewhich the atraumatic tip portion 134 can flex, can be increased ordecreased by decreasing or increasing the diameter of the rod 140. Inaddition, the flexibility of the rod 140 can be altered by making therod 140 from a stiff or flexible material.

In some embodiments as illustrated in FIGS. 2A and 3A, a reflectivesurface 144 is disposed on the proximal end of the rod 140, which isinserted into the optical fiber 130. The reflective surface 144 iscapable of reflecting back at least a portion of either reference lightor excitation light emitted from the light source. The other end of therod 140 is inserted into the atraumatic tip portion 134. In certainembodiments, the atraumatic tip portion may be made from anon-reflective material, for example polyethylene (e.g., blackpolyethylene) or polypropylene. The reference or excitation light thatpasses though the optical fiber 130 in the region corresponding to thediameter of the rod 140 is reflected off the reflective surface 144without entering into the hydrogel filled cavity 116; the amount oflight entering the hydrogel/chemical indicator system can be controlledby varying the diameter/cross-sectional area of the rod and/or byattaching a minor or other reflective member 190 (illustrated in FIGS. 5and 6) having a selected cross-sectional area to the proximal end of therod. The hydrogel filled cavity 116 is preferably covered by aselectively permeable membrane 142, which is at least permeable toglucose. Therefore, the reflected reference or excitation light and theratio between the reflected and emitted light is independent of thetemperature, pH, glucose concentration, and chemistry formulation of thehydrogel filled cavity 116. The ratio between the reflected and emittedlight is dependent, however, on the diameter of the rod and the ratio ofthe diameter of the rod to the area of the sensor. In certainembodiments, the rod 140 is sufficiently stiff to keep the hydrogelfilled cavity 116 in a fixed orientation relative to the optical fiber130 so that any light that is transmitted through the hydrogel cavity116 is not reflected back to the optical fiber 130.

With regard to FIG. 3B, there is shown a perspective view of the distalregion of the sensor 117 illustrated in FIG. 3A. It can be appreciatedin the illustrated embodiment that there is no change in sensor diameterfrom the optical fiber 130, through the membrane 142 covered hydrogelcavity, until the tapered atraumatic distal tip portion 134.

In some embodiments, as shown in FIG. 4, a window 180 is cut into ahypotube 140. The distal end 132 of the optical fiber 130 is insertedonto the reflective surface 144 (e.g., an annular minor) and then heatedsuch that the optical fiber 130 swells to fully contact the reflectivesurface 144 of the hypotube 140. In certain embodiments, heating theoptical fiber 130 is carried out in a glass tube. In other embodiments,heating the optical fiber 130 is carried out in an oven. In still otherembodiments, the optical fiber 130 is attached to the hypotube 140 usingan adhesive. In preferred embodiments, the adhesive is biocompatible,such as for example, cyanoacrylates, epoxies, light cure adhesives,silicones, and urethanes. In certain embodiments, after applying theadhesive and attaching the optical fiber 130 to the hypotube 140, theadhesive is cured at room temperature, by heating, or by applyingUV/visible light. In certain embodiments, the time to adhere the opticalfiber 130 to the hypotube 140 can vary from about 5 seconds to about 60seconds, from about 15 minutes to about 5 hours, from about 60 secondsto about 10 minutes, or up to about 24 hours. Similar methods may beemployed for attaching the hypotube 140 to the atraumatic tip 134.Similar to previous embodiments, the reference or excitation light isreflected off the reflective surface 144 without entering the window 180that opens to the cavity 116 which is filled with hydrogel/chemicalindicator system. Therefore, the reflected reference or excitation lightand the ratio between the reflected and emitted lights is independent ofthe temperature, pH, glucose concentration, and hydrogel chemistry. Thesurface area of the reflective surface can be varied to control theamount of excitation light that enters the hydrogel/chemical indicatorsystem filed cavity 116. The distal end 136 of the hypotube 140, as inprevious embodiments, may have a non-reflective surface, such as a blackplug made of polyethylene so that light entering the hydrogel/chemicalindicator system filled cavity 116 is not reflected back into theoptical fiber 130. In some embodiments, the window 180 containing thehydrogel/chemical indicator system filled cavity 116 is covered by aselectively permeable membrane (not shown).

In some embodiments, as illustrated in FIG. 5, the glucose sensor 117includes a cage 195, as an outer shell, connecting the atraumatic tip134 with the optical fiber 130. The cage 195 can add mechanicalstability to the distal portion of the sensor 117. In some embodiments,the cage 195 also adds flexibility to the distal portion of the sensor117, allowing the atraumatic tip portion 134 to flex back and forthrelative to the orientation of the optical fiber 130. The flexibility ofthe cage 195, and thus the degree which the atraumatic tip portion 134can flex, can be increased or decreased by decreasing or increasing thethickness of the cage 195 walls. In addition, the flexibility of thecage 195 can be altered by making the cage 195 from a stiff or flexiblematerial. In certain embodiments, the thickness of the cage 195 walls isabout 0.001 inches, about 0.002 inches, or about 0.004 inches. In someembodiments, the thickness of the cage 195 walls may be less than about0.001 inches. In some embodiments, the thickness of the cage 195 wallsmay be greater than about 0.010 inches.

In some embodiments, the diameter of the optical fiber 130 may besmaller than the diameter of the interior of the cage 195, allowing theoptical fiber 130 to fit within the interior of the cage 195 and abutthe void or cavity 116. For example, the diameter of the optical fiber130 may be between about 0.005 inches and about 0.020 inches, betweenabout 0.008 inches and about 0.014 inches, or between about 0.010 inchesand about 0.012 inches. The diameter of the interior of the cage 195 maybe about 0.001 inches larger.

In certain embodiments, the cage 195 has a window or opening 180,covered by a selectively permeable membrane 142 (not shown), whichallows for at least the transmission of analytes, such a glucose, intothe void or cavity 116. In certain preferred embodiments, the void orcavity 116 is filled with a hydrogel/chemical indicator system. A rod140 may be positioned within the glucose sensor 117 having a referencematerial 190. As discussed above, the reference material 190 may be aminor for reflecting excitation light from the optical fiber 130 back toa detector (not shown) or a glucose-insensitive fluorescent dye foremitting a glucose-insensitive reference signal back to a detector (notshown). The combination of the cage 195 and the rod 140 may provide asufficiently rigid structure such that the excitation light which entersthe void or cavity 116 remains separate from the light that enters thereference material 190.

In some embodiments, as illustrated in FIG. 6, the glucose sensor 117does not have a cage 195 surrounding the void or cavity 116. Instead,similar to FIGS. 2A and 3A, the rod 140 connects the optical fiber 130and atraumatic tip 134, providing structure for the glucose sensor 117,and is surrounded by the void or cavity 116, which in turn is covered bya selectively permeable membrane 142. Similar to FIG. 3A, the diameterof the optical fiber 130 is the same as the diameter of thehydrogel/chemical indicator system encased cavity 116. As discussed withrespect to FIG. 5, the rod may have a reference material 190 attached tothe proximal surface of the rod 144, which functions as previouslydiscussed.

FIGS. 7-11 illustrate certain embodiments having differentconfigurations for the reference material 190. As discussed previously,the reference material 190 in each of these embodiments may eithercomprise reflective material to return at least a portion of theexcitation light back to a detector (not shown) or a separate dyeindicator system to return an emission signal back to a detector (notshown). Similar to previous embodiments, the excitation or referencelight is reflected off the reflective surface 190 without entering thecavity 116, which is filled with the hydrogel/chemical indicator system.Likewise, the emitted or reference light from the separate dye indicatorsystem is independent of the glucose concentration. Therefore, thereference light and the ratio between the reference light and emittedglucose concentration dependent lights are independent of thetemperature, pH, glucose concentration, and hydrogel chemistry. Thesurface area, shape, and configuration of the reference material 190 canbe varied to control the amount of excitation light that enters thehydrogel/chemical indicator system filed cavity 116. The distal end 136of the rod or hypotube 140, as in previous embodiments, or referencematerial 190 may have a non-reflective surface, such as a black plugmade of polyethylene so that light entering the hydrogel/chemicalindicator system filled cavity 116 is not reflected back into theoptical fiber 130.

In FIG. 7, the reference material 190 abuts the void or cavity 116beneath the cage 195 and extends to and comprises the atraumatic tip134. In certain embodiments, the atraumatic tip 134 is formed of aglucose-insensitive red dye plastic material. In FIG. 8, the referencematerial 190 is a reflective strip that spans the diameter of thehydrogel-filled cavity 116. The term reflective strip is used herein torefer to any elongate member, regardless of its geometry, width, orthickness that spans at least a cross-section of the glucose sensor 117.The reflective strip 190 may be centered at the diameter of the glucosesensor 117 (as illustrated) or off-centered with regard to thecross-section of the cage 195 or optical fiber 130. In some embodiments,there may be more than one reflective strip in one or more locationswithin the glucose sensor 117. Where more than one reflective strip isemployed, the reflective strip may be arranged symmetrically orasymmetrically with respect to the cross-section of the glucose sensor117. In certain embodiments, the reflective strip 190 may be betweenabout 0.001 inches and about 0.005 inches wide and between about 0.001inches and about 0.005 inches thick.

In FIG. 9, the reference material 190 is disposed within the cage 195 asa hypotube containing the hydrogel-filled cavity 116 and having areflective surface or annular minor at the proximal surface of thehypotube 144. In certain embodiments, the hypotube 144 has an outerdiameter equal to the outer diameter of the optical fiber 130. In FIG.10, similar to FIG. 8, the reference material 190 is reflective strip,but the reflective strip in FIG. 10 is placed within a hole drilled inthe optical fiber 130, rather than the abutting the hydrogel-filledcavity 116. FIG. 11 illustrates an embodiment in which the referencematerial 190 is located in the cavity 116 and is in a side-by-sideconfiguration with the hydrogel/chemical indicator system.

In certain embodiments, as illustrated in FIG. 12, a reference material200 comprises a translucent material. In certain embodiments, thistranslucent material comprises a red dye, such as theglucose-insensitive fluorescent dye discussed previously. The red dyemay allow some of the excitation light to be transmitted to thehydrogel-filled cavity 116, may reflect some of the excitation lightback to a detector (not shown) before the excitation light reaches thehydrogel-filled cavity 116, and may emit a separate glucose-insensitivesignal to a detector (not shown).

A person skilled in the art would readily understand that the abovedescribed embodiments, or components of the above described embodiments,may be combined within the scope of the present invention. For example,a glucose sensor may contain one or more structural elements, such as acage, a hypotube, and/or a rod within the scope of the presentinvention. In addition, a glucose sensor may contain one or morereference materials, functioning as a reflective surface and/or as aseparate dye indicator system, in different locations and configurationswithin the scope of the present invention.

In some embodiments (see e.g., FIGS. 2-12), the glucose sensor 117comprises an atraumatic tip portion 134. The atraumatic tip portion 134has a distal end 138 that is curved and substantially free of sharpedges. In addition, the atraumatic tip portion 134 can be flexible anddeformable. The distal end 138 of the atraumatic tip portion 134 can behemispherical, parabolic, elliptical or curved in any other suitableshape that is reduces the risk of injury to the patient. The atraumatictip portion 134 can be made from a variety of materials, such asplastics, polymers, gels, metals and composites of the above.

In some embodiments, the glucose sensor 117 includes a temperaturesensor or probe 146, such as thermocouple or thermistor (See e.g., FIG.2A). The temperature sensor 146 can measure the temperature of thehydrogel and glucose sensing chemistry system, and/or the blood whendisposed intravascularly. The temperature sensor 146 is particularlypreferred when the glucose-sensing chemistry is affected by temperature.For example, in some embodiments, the fluorescence intensity emitted bythe fluorophore system is dependent on the temperature of thefluorophore system. By measuring the temperature of the fluorophoresystem, temperature induced variations in fluorophore fluorescenceintensity can be accounted for, allowing for more accurate determinationof glucose concentration.

In certain embodiments, the temperature sensor can be a thermistor (asdescribed above with regard to FIG. 2, reference numeral 146, a platinumresistance temperature device (“RTD”), another RTD, a thermocouple, aninfrared-based temperature detector, a fluorescence-based temperaturesensing element, or other temperature sensing elements with determinabletemperature-dependent characteristics.

Devices such as thermistors, platinum RTDs, and other RTDs generallyrequire one or more conductors, such as wires, to conduct the output ofthe sensor to a receiving unit which converts the output to atemperature signal. The conductors can be bundled with the optical fiberof fluorescence-based glucose sensors, such as those discussed above, orthey can be routed separately. In one embodiment, the temperature sensoris placed inside the body, and the receiver is placed outside the body.In another embodiment, the temperature sensor is placed inside the body,and a transmitter, signal processor, etc. is also placed inside the bodyand is connected to or is a part of the temperature sensor. In preferredembodiments, the temperature sensing element is located at or near theglucose sensing moiety.

In another embodiment, a fluorescence-based temperature sensingtechnique can be used. Fluorescence-based temperature sensing techniquesinclude those based on fluorescence decay, such as where an excitationlight is provided to a phosphor, the excitation light is stopped, andthe fluorescence is monitored versus time, with the rate of decrease influorescence being related to the temperature of the phosphor. Varioustechniques, can also include phase measurement and phase angle analysis.

Methods for performing fluorescence-based temperature measurement havebeen described. See for example, LumaSense Technologies, Inc. (SantaClara, Calif.), “Fluoroptic Temperature Monitoring,”http://www.lumasenseinc.com/technology/fluoroptic_thermometry.html.Fluorescent materials that can be used in fluorescence-based temperaturemeasurement are known to, or readily identified by those having skill inthe art.

In some embodiments, the fluorescent material can be surrounded bymaterial which prevents or inhibits chemical interaction between thefluorescent material and blood components. Suitable materials includeglass (for example, borosilicate, lime-soda, or other types includingthose used for fiberoptic cables), polymers (for example, Teflon,fluoropolymers, silicone, latex, polyolefins, polyisoprene, and otherrigid and nonrigid polymeric materials), metals (for example, 300 seriesstainless steel, 400 series stainless steel, nickel, nickel alloys,chromium steels, zirconium and its alloys, titanium and its alloys, aswell as other corrosion resistant metals and alloys including exoticmetals and alloys), ceramics (for example, ceramic materials related toaluminum oxide, silica and oxide, zirconium, carbides, etc.), andcombinations of these.

In some embodiments, the temperature sensor can be positioned within theglucose sensor, or near it. While in one preferred embodiment, thetemperature sensor can be positioned as close as possible to (e.g.,within) the glucose-sensing chemical indicator system of the glucosesensor, positions some distance away can also be successfully utilized,including those locations where the temperature measured provides anindication of the temperature at the glucose-sensing site(s) within anacceptable error for the use for which the temperature measurement isbeing made.

In some embodiments, the temperature sensor and/or the leads to thesensor can be isolated from the physiological environment, such as bycoating, covering, or encasing the various parts with a material thatprevents or inhibits chemical or physical interaction between thetemperature sensor and/or its leads and blood components. Chemicalinteractions that are preferably avoided include corrosion, leaching ofchemical species, generation of additional signals (e.g. optical,electrical, etc.) and take-up by the body of materials present in thesensor or leads, whether present from manufacture, corrosion or othermeans, such as compounds, metals, or ions causing a physiologicalresponse in some patients including copper, silver, organic compounds,organometallic compounds, etc.

Physical interactions can include breakage and physical separation (e.g.disconnection and potential loss), signal leakage (e.g. optical;electrical, etc.), signal degradation (including resistance, straysignal detection, noise, capacitance, electrochemical effects, inducedvoltages, ground loops, etc.). Suitable materials include glass (e.g.,borosilicate, lime-soda, as well as other types of glass, such as thoseused in production of optic fibers), polymers (e.g., Teflon,fluoropolymers, silicone, latex, polyolefins, polyisoprene, acrylics,polycarbonates, and other rigid and nonrigid polymeric materials),metals (e.g., 300 series stainless steel, 400 series stainless steel,nickel, nickel alloys, chromium steels, zirconium and its alloys,titanium and its alloys, as well as other corrosion resistant metals andalloys including exotic metals and alloys), ceramics (e.g., ceramicmaterials related to aluminum oxide, silica and oxide, zirconium,carbides, etc.), and combinations of these.

Suitable methods for applying for isolating material to the temperaturesensor or leads can include any appropriate method, including casting,painting, dipping, gluing, reacting, drawing, depositing, mechanicallyadhering, encapsulating, etc.

In some embodiments, suitable sizes for temperature sensors that will beincorporated into the glucose sensor include those temperature sensingelements resulting in an overall glucose sensor of between about 0.005inches and 0.020 inches.

FIG. 13 illustrates another embodiment for measuring the glucoseconcentration in comparison to a reference signal. In this embodiment, aLED source 1300 sends an excitation signal down two separate adjacentoptical fibers 1310, 1320. The first optical fiber, or the glucose fiber1310, has a proximal tip and a distal tip. The distal tip has a glucosesensing hydrogel 1330 which contains a fluorophore or dye, a quencher,and glucose binding receptors. The second optical fiber, or thereference fiber 1320, also has a proximal tip and a distal tip. Thedistal tip of the reference fiber has a reference material 1340. Incertain embodiments, the reference material 1340 contains the same or adifferent fluorophore or dye, may or may not contain the quencher, butdoes not contain glucose receptors. In other embodiments, the referencematerial 1340 has the same exact glucose sensing hydrogel, but it isencased in a glucose impermeable membrane. In both of these embodiments,the reference fiber 1320 emits a fluorescent return signal independentof the glucose concentration.

After the excitation light passes through the glucose fiber 1310 and thereference fiber 1320, the glucose sensing hydrogel 1330 and thereference material 1340 emit fluorescent signals back to two separatedetectors, a glucose signal detector 1350 and a reference signaldetector 1360, for ratiometric processing. The benefit of the dual fiberconfiguration is that both fibers 1310, 1320 experience the sameexternal pressure, bending, temperature, and other external factors. Inaddition, both fibers 1310, 1320 contain substantially the same materialin the glucose sensing hydrogel 1330 and reference material 1340. As aresult, the ratio of the intensities between the two fibers 1310, 1320,as measured by the detectors 1350, 1360, produce a calibrated glucosesignal that removes, inter alia, the effect of the fluctuations in theLED output or altered transmission along the optical fiber, and therebyincrease the accuracy in the measurement of the glucose concentration.

With reference to FIG. 14, in certain embodiments, the light generatedby the single light source 401 is transmitted through a optical modulecomprising a collimator lens 402, an interference filter 403, and/or afocusing lens 404 as described above. The resulting light can befiltered through an interference filter 403. The resulting light can befocused by a focusing lens 404 into an optical fiber 405, which may be asingle fiber or a bundle of fibers. The optical fiber 405 can surroundoptical fiber 410 as both fiber optic lines connect to the first end ofthe glucose sensor 407. In certain embodiments, a mirror or reflectivesurface 409 is attached to the second end of the glucose sensor 407. Theoptical fiber 410 may be a single fiber or a bundle of fibers. Theglucose sensor can comprise hydrogels that further comprise afluorophore system that produces two emission wavelengths, a firstemission wavelength and a second emission wavelength. In certainembodiments, the fluorophore system is excited by the light generated bylight source 401. In certain embodiments, the optical fiber 410 isconnected to a light sensitive module comprising a microspectrometer 411that measures the entire spectrum of light in the glucose measurementsystem 400. Data from the microspectrometer 411 can be transmitted tocomputer 412 for processing. The microspectrometer 411 can allow system400 to simultaneously measure the excitation light intensity as well asboth emission light intensities. Ratiometric calculations may beemployed to substantially eliminate or reduce non-glucose relatedfactors affecting the intensity of the measured emission light andmeasured excitation light (as detailed in US Patent Publication No.2008/0188725; incorporated herein in its entirety by reference thereto).The measured emission light can be divided by the measured excitationlight, wherein such calculations substantially eliminate or reducenon-glucose related factors affecting the intensity of the lights.

In certain preferred embodiments, the fluorophore dye may be selectedsuch that it exists in distinguishable acid and base conformations, eachof which emit at a distinct wavelength, and wherein the relativeproportion of acid and base forms depend on the pH. The ratio ofintensities of the acid and base emissions can be used to determine thepH of the blood (as detailed in US Patent Publication No. 2008/0188722;incorporated herein in its entirety by reference thereto). The ratio ofthe acid or base emission intensity over the excitation light can beused to determine the level of glucose in the blood. Of course in avariation to this single exciter-dual emitter fluorophore system, onecould employ a single exciter-single emitter for detection of glucoseconcentration without simultaneous ratiometric determination of pH.Indeed, a great variety of design options are available (see e.g., USPatent Publication Nos. 2008/0188725 and 2008/0188722), wherein thechemical indicator and optical systems may be selected based on thepreferred use.

Glucose-Sensing Chemical Indicator Systems

In certain embodiments, the hydrogels are associated with a plurality offluorophore systems. In certain embodiments, the fluorophore systemscomprise a quencher with a glucose receptor site. In certainembodiments, when there is no glucose present to bind with the glucosereceptor, the quencher prevents the fluorophore system from emittinglight when the dye is excited by an excitation light. In certainembodiments, when there is glucose present to bind with the glucosereceptor, the quencher allows the fluorophore system to emit light whenthe dye is excited by an excitation light.

In certain embodiments, the emission produced by the fluorophore systemmay vary with the pH (as well as the temperature) of the solution (forexample, blood), such that different excitation wavelengths (oneexciting the acid form of the fluorophore and the other the base form ofthe fluorophore) produce different emissions signals. In preferredembodiments, the ratio of the emission signal from the acid form of thefluorophore over the emission signal from the base form of thefluorophore is related to the pH level of the blood. In certainembodiments, an interference filter is employed to ensure that the twoexcitation lights are exciting only one form (the acid form or the baseform) of the fluorophore. Chemical indicator systems, hardwareconfigurations and methods for determining both pH and glucose based onratiometric determination are described in detail in co-pending U.S.application Ser. Nos. 11/671,880 (published as 2008/0188722) and12/027,158 (published as 2008/0188725); incorporated herein in theirentirety by reference thereto.

The indicator system (also referred to herein as a fluorophore system)can comprise a fluorophore operably coupled to a quencher. In certainembodiments, the fluorophore system comprises a polymer matrixcomprising a fluorophore susceptible to quenching by a viologen, aviologen quencher with quenching efficacy dependent on glucoseconcentration, and a glucose permeable polymer, wherein said matrix isin contact with blood in vivo. Preferably the fluorophore is afluorescent organic dye, the quencher is a boronic acid functionalizedviologen, and the matrix is a hydrogel.

“Fluorophore” refers to a substance that when illuminated by light at aparticular wavelength emits light at a longer wavelength; i.e. itfluoresces. Fluorophores include but are not limited to organic dyes,organometallic compounds, metal chelates, fluorescent conjugatedpolymers, quantum dots or nanoparticles and combinations of the above.Fluorophores may be discrete moieties or substituents attached to apolymer.

Fluorophores that may be used in preferred embodiments are capable ofbeing excited by light of wavelength at or greater than about 400 nm,with a Stokes shift large enough that the excitation and emissionwavelengths are separable by at least 10 nm. In some embodiments, theseparation between the excitation and emission wavelengths may be equalto or greater than about 30 nm. These fluorophores are preferablysusceptible to quenching by electron acceptor molecules, such asviologens, and are resistant to photo-bleaching. They are alsopreferably stable against photo-oxidation, hydrolysis andbiodegradation.

In some embodiments, the fluorophore may be a discrete compound.

In some embodiments, the fluorophore may be a pendant group or a chainunit in a water-soluble or water-dispersible polymer having molecularweight of about 10,000 daltons or greater, forming a dye-polymer unit.In one embodiment, such dye-polymer unit may also be non-covalentlyassociated with a water-insoluble polymer matrix M¹ and is physicallyimmobilized within the polymer matrix M¹, wherein M¹ is permeable to orin contact with an analyte solution. In another embodiment, the dye onthe dye-polymer unit may be negatively charged, and the dye-polymer unitmay be immobilized as a complex with a cationic water-soluble polymer,wherein said complex is permeable to or in contact with the analytesolution. In one embodiment, the dye may be one of the polymericderivatives of hydroxypyrene trisulfonic acid. The polymeric dyes may bewater-soluble, water-swellable or dispersible in water. In someembodiments, the polymeric dyes may also be cross-linked. In preferredembodiments, the dye has a negative charge.

In other embodiments, the dye molecule may be covalently bonded to thewater-insoluble polymer matrix M¹, wherein said M¹ is permeable to or incontact with the analyte solution. The dye molecule bonded to M¹ mayform a structure M¹-L¹-Dye. L¹ is a hydrolytically stable covalentlinker that covalently connects the sensing moiety to the polymer ormatrix. Examples of L¹ include lower alkylene (e.g., C₁-C₈ alkylene),optionally terminated with or interrupted by one or more divalentconnecting groups selected from sulfonamide (—SO₂NH—), amide —(C═O)N—,ester —(C═O)—O—, ether. —O—, sulfide —S—, sulfone (—SO₂—), phenylene—C₆H₄—, urethane —NH(C═O)—O—, urea —NH(C═O)NH—, thiourea —NH(C═S)—NH—,amide —(C═O)NH—, amine —NR— (where R is defined as alkyl having 1 to 6carbon atoms) and the like, or a combination thereof. In one embodiment,the dye is bonded to a polymer matrix through the sulfonamide functionalgroups.

In one preferred embodiment, the fluorophore may be HPTS-CysMA(structure illustrated below); see U.S. Pat. No. 7,417,164, incorporatedin its entirety herein by reference thereto.

Of course, in some embodiments, substitutions other than Cys-MA on theHPTS core are consistent with aspects of the present invention, as longas the substitutions are negatively charged and have a polymerizablegroup. Either L or D stereoisomers of cysteine may be used. In someembodiments, only one or two of the sulfonic acids may be substituted.Likewise, in variations to HPTS-CysMA shown above, other counterionsbesides NBu₄ ⁺ may be used, including positively charged metals, e.g.,Na⁺. In other variations, the sulfonic acid groups may be replaced withe.g., phosphoric, carboxylic, etc. functional groups.

Fluorescent dyes, including HPTS and its derivatives are known and manyhave been used in analyte detection. See e.g., U.S. Pat. Nos. 6,653,141,6,627,177, 5,512,246, 5,137,833, 6,800,451, 6,794,195, 6,804,544,6,002,954, 6,319,540, 6,766,183, 5,503,770, and 5,763,238; each of whichis incorporated herein in its entirety by reference thereto.

In accordance with broad aspects of the present invention, the analytebinding moiety provides the at least dual functionality of being able tobind analyte and being able to modulate the apparent concentration ofthe fluorophore (e.g., detected as a change in emission signalintensity) in a manner related to the amount of analyte binding. Inpreferred embodiments, the analyte binding moiety is associated with aquencher. “Quencher” refers to a compound that reduces the emission of afluorophore when in its presence. Quencher (Q) is selected from adiscrete compound, a reactive intermediate which is convertible to asecond discrete compound or to a polymerizable compound or Q is apendant group or chain unit in a polymer prepared from said reactiveintermediate or polymerizable compound, which polymer is water-solubleor dispersible or is an insoluble polymer, said polymer is optionallycrosslinked.

In one example, the moiety that provides glucose recognition in theembodiments is an aromatic boronic acid. The boronic acid is covalentlybonded to a conjugated nitrogen-containing heterocyclic aromaticbis-onium structure (e.g., a viologen). “Viologen” refers generally tocompounds having the basic structure of a nitrogen containing conjugatedN-substituted heterocyclic aromatic bis-onium salt, such as 2,2′-, 3,3′-or 4,4′-N,N′ bis-(benzyl) bipyridium dihalide (i.e., dichloride, bromidechloride), etc. Viologen also includes the substituted phenanthrolinecompounds. The boronic acid substituted quencher preferably has a pKa ofbetween about 4 and 9, and reacts reversibly with glucose in aqueousmedia at a pH from about 6.8 to 7.8 to form boronate esters. The extentof reaction is related to glucose concentration in the medium. Formationof a boronate ester diminishes quenching of the fluorophore by theviologen resulting in an increase in fluorescence dependent on glucoseconcentration. A useful bis-onium salt is compatible with the analytesolution and capable of producing a detectable change in the fluorescentemission of the dye in the presence of the analyte to be detected.

Bis-onium salts in the embodiments of this invention are prepared fromconjugated heterocyclic aromatic di-nitrogen compounds. The conjugatedheterocyclic aromatic di-nitrogen compounds are selected fromdipyridyls, dipyridyl ethylenes, dipyridyl phenylenes, phenanthrolines,and diazafluorenes, wherein the nitrogen atoms are in a differentaromatic ring and are able to form an onium salt. It is understood thatall isomers of said conjugated heterocyclic aromatic di-nitrogencompounds in which both nitrogens can be substituted are useful in thisinvention. In one embodiment, the quencher may be one of the bis-oniumsalts derived from 3,3′-dipyridyl, 4,4′-dipyridyl and4,7-phenanthroline.

In some embodiments, the viologen-boronic acid adduct may be a discretecompound having a molecular weight of about 400 daltons or greater. Inother embodiments, it may also be a pendant group or a chain unit of awater-soluble or water-dispersible polymer with a molecular weightgreater than about 10,000 daltons. In one embodiment, thequencher-polymer unit may be non-covalently associated with a polymermatrix and is physically immobilized therein. In yet another embodiment,the quencher-polymer unit may be immobilized as a complex with anegatively charge water-soluble polymer.

In other embodiments, the viologen-boronic acid moiety may be a pendantgroup or a chain unit in a crosslinked, hydrophilic polymer or hydrogelsufficiently permeable to the analyte (e.g., glucose) to allowequilibrium to be established.

In other embodiments, the quencher may be covalently bonded to a secondwater-insoluble polymer matrix M², which can be represented by thestructure M²-L²-Q. L² is a linker selected from the group consisting ofa lower alkylene (e.g., C₁-C₈ alkylene), sulfonamide, amide, quaternaryammonium, pyridinium, ester, ether, sulfide, sulfone, phenylene, urea,thiourea, urethane, amine, and a combination thereof. The quencher maybe linked to M² at one or two sites in some embodiments.

In certain embodiments, at least one quencher precursor is used toattach the quenching moiety to at least one polymer. For example,aromatic groups may be used to functionalize a viologen withcombinations of boronic acid groups and reactive groups. In certainembodiments, this process includes attaching an aromatic group to eachof the two nitrogens in the dipyridyl core of the viologen. At least oneboronic acid group, a reactive group, or a combination of the two arethen attached to each aromatic group, such that the groups attached toeach of the two nitrogens on the dipyridyl core of the viologen mayeither be the same or different. Certain combinations of thefunctionalized viologen quenching moiety are described as follows:

-   -   a) a first aromatic group having a pendent reactive group is        attached to the first nitrogen and a second aromatic group        having at least one pendent boronic group is attached to the        second nitrogen;    -   b) one or more boronic acid groups are attached to a first        aromatic group, which is attached to the first nitrogen, and one        boronic acid group and a reactive group are attached to a second        aromatic group, which second aromatic group is attached to the        second nitrogen;    -   c) one boronic acid group and a reactive group are attached to a        first aromatic group, which first aromatic group is attached to        the first nitrogen, and one boronic acid group and a reactive        group are attached to a second aromatic group, which is attached        to the second nitrogen; and    -   d) one boronic acid group is attached to an aromatic group,        which aromatic group is attached to each of the two nitrogens,        and a reactive group is attached to a carbon in a heteroaromatic        ring in the heteroaromatic centrally located group.

Preferred embodiments comprise two boronic acid moieties and onepolymerizable group or coupling group wherein the aromatic group is abenzyl substituent bonded to the nitrogen and the boronic acid groupsare attached to the benzyl ring and may be in the ortho- meta- orpara-positions.

In one preferred embodiment, the quencher precursor (beforeincorporation into a hydrogel) may be 3,3′-oBBV (structure illustratedbelow); see U.S. Pat. No. 7,470,420, incorporated in its entirety hereinby reference thereto.

The quencher precursor 3,3′-oBBV may be used with HPTS-CysMA to makehydrogels in accordance with preferred aspects of the invention.

Other indicator chemistries, such as those disclosed in U.S. Pat. No.5,176,882 to Gray et al. and Pat. No. 5,137,833 to Russell, can also beused in accordance with embodiments of the present invention; both ofwhich are incorporated herein in their entireties by reference thereto.In some embodiments, an indicator system may comprise an analyte bindingprotein operably coupled to a fluorophore, such as the indicator systemsand glucose binding proteins disclosed in U.S. Pat. Nos. 6,197,534,6,227,627, 6,521,447, 6,855,556, 7,064,103, 7,316,909, 7,326,538,7,345,160, and 7,496,392, U.S. Patent Application Publication Nos.2003/0232383, 2005/0059097, 2005/0282225, 2009/0104714, 2008/0311675,2008/0261255, 2007/0136825, 2007/0207498, and 2009/0048430, and PCTInternational Publication Nos. WO 2009/021052, WO 2009/036070, WO2009/021026, WO 2009/021039, WO 2003/060464, and WO 2008/072338 whichare hereby incorporated by reference herein in their entireties.

For in vivo applications, the sensor is used in a moving stream ofphysiological fluid which contains one or more polyhydroxyl organiccompounds or is implanted in tissue such as muscle which contains saidcompounds. Therefore, it is preferred that none of the sensing moietiesescape from the sensor assembly. Thus, for use in vivo, the sensingcomponents are preferably part of an organic polymer sensing assembly.Soluble dyes and quenchers can be confined by a selectively permeablemembrane that allows passage of the analyte but blocks passage of thesensing moieties. This can be realized by using as sensing moietiessoluble molecules that are substantially larger than the analytemolecules (molecular weight of at least twice that of the analyte orgreater than 1000 preferably greater than 5000); and employing aselective semipermeable membrane such as a dialysis or anultrafiltration membrane with a specific molecular weight cutoff betweenthe two so that the sensing moieties are quantitatively retained.

Preferably the sensing moieties are immobilized in an insoluble polymermatrix, which is freely permeable to glucose. The polymer matrix iscomprised of organic, inorganic or combinations of polymers thereof. Thematrix may be composed of biocompatible materials. Alternatively, thematrix is coated with a second biocompatible polymer that is permeableto the analytes of interest.

The function of the polymer matrix is to hold together and immobilizethe fluorophore and quencher moieties while at the same time allowingcontact with the analyte, and binding of the analyte to the boronicacid. To achieve this effect, the matrix must be insoluble in themedium, and in close association with it by establishing a high surfacearea interface between matrix and analyte solution. For example, anultra-thin film or microporous support matrix is used. Alternatively,the matrix is swellable in the analyte solution, e.g. a hydrogel matrixis used for aqueous systems. In some instances, the sensing polymers arebonded to a surface such as the surface of a light conduit, orimpregnated in a microporous membrane. In all cases, the matrix must notinterfere with transport of the analyte to the binding sites so thatequilibrium can be established between the two phases. Techniques forpreparing ultra-thin films, microporous polymers, microporous sol-gels,and hydrogels are established in the art. All useful matrices aredefined as being analyte permeable.

Hydrogel polymers are used in some embodiments. The term, hydrogel, asused herein refers to a polymer that swells substantially, but does notdissolve in water. Such hydrogels may be linear, branched, or networkpolymers, or polyelectrolyte complexes, with the proviso that theycontain no soluble or leachable fractions. Typically, hydrogel networksare prepared by a crosslinking step, which is performed on water-solublepolymers so that they swell but do not dissolve in aqueous media.Alternatively, the hydrogel polymers are prepared by copolymerizing amixture of hydrophilic and crosslinking monomers to obtain a waterswellable network polymer. Such polymers are formed either by additionor condensation polymerization, or by combination process. In thesecases, the sensing moieties are incorporated into the polymer bycopolymerization using monomeric derivatives in combination withnetwork-forming monomers. Alternatively, reactive moieties are coupledto an already prepared matrix using a post polymerization reaction. Saidsensing moieties are units in the polymer chain or pendant groupsattached to the chain.

The hydrogels useful in this invention are also monolithic polymers,such as a single network to which both dye and quencher are covalentlybonded, or multi-component hydrogels. Multi-component hydrogels includeinterpenetrating networks, polyelectrolyte complexes, and various otherblends of two or more polymers to obtain a water swellable composite,which includes dispersions of a second polymer in a hydrogel matrix andalternating microlayer assemblies.

Monolithic hydrogels are typically formed by free radicalcopolymerization of a mixture of hydrophilic monomers, including but notlimited to HEMA, PEGMA, methacrylic acid, hydroxyethyl acrylate, N-vinylpyrrolidone, acrylamide, N,N′-dimethyl acrylamide, and the like; ionicmonomers include methacryloylaminopropyl trimethylammonium chloride,diallyl dimethyl ammonium. chloride, vinyl benzyl trimethyl ammoniumchloride, sodium sulfopropyl methacrylate, and the like; crosslinkersinclude ethylene dimethacrylate, PEGDMA, trimethylolpropane triacrylate,and the like. The ratios of monomers are chosen to optimize networkproperties including permeability, swelling index, and gel strengthusing principles well established in the art. In one embodiment, the dyemoiety is derived from an ethylenically unsaturated derivative of a dyemolecule, such as8-acetoxypyrene-1,3,6-N,N′,N″-tris(methacrylamidopropylsulfonamide), thequencher moiety is derived from an ethylenically unsaturated viologensuch as 4-N-(benzyl-3-boronicacid)-4′-N′-(benzyl-4-ethenyl)-dipyridinium dihalide (m-SBBV) and thematrix is made from HEMA and PEGDMA. The concentration of dye is chosento optimize emission intensity. The ratio of quencher to dye is adjustedto provide sufficient quenching to produce the desired measurablesignal.

In some embodiments, a monolithic hydrogel is formed by a condensationpolymerization. For example, acetoxy pyrene trisulfonyl chloride isreacted with an excess of PEG diamine to obtain a tris-(amino PEG)adduct dissolved in the unreacted diamine. A solution of excesstrimesoyl chloride and an acid acceptor is reacted with4-N-(benzyl-3-boronic acid)-4′-N′-(2 hydroxyethyl) bipyridinium dihalideto obtain an acid chloride functional ester of the viologen. The tworeactive mixtures are brought into contact with each other and allowedto react to form the hydrogel, e.g. by casting a thin film of onemixture and dipping it into the other.

In other embodiments, multi-component hydrogels wherein the dye isincorporated in one component and the quencher in another are preferredfor making the sensor of this invention. Further, these systems areoptionally molecularly imprinted to enhance interaction betweencomponents and to provide selectivity for glucose over other polyhydroxyanalytes. Preferably, the multicomponent system is an interpenetratingpolymer network (IPN) or a semi-interpenetrating polymer network(semi-IPN).

The IPN polymers are typically made by sequential polymerization. First,a network comprising the quencher is formed. The network is then swollenwith a mixture of monomers including the dye monomer and a secondpolymerization is carried out to obtain the IPN hydrogel.

The semi-IPN hydrogel is formed by dissolving a soluble polymercontaining dye moieties in a mixture of monomers including a quenchermonomer and through complex formation with the fluorophore. In someembodiments, the sensing moieties are immobilized by an insolublepolymer matrix which is freely permeable to polyhydroxyl compounds.Additional details on hydrogel systems have been disclosed in US PatentPublications Nos. US2004/0028612, and 2006/0083688 which are herebyincorporated by reference in their entireties.

The polymer matrix is comprised of organic, inorganic or combinations ofpolymers thereof. The matrix may be composed of biocompatible materials.Alternatively, the matrix is coated with a second biocompatible polymerthat is permeable to the analytes of interest. The function of thepolymer matrix is to hold together and immobilize the fluorescent dyeand quencher moieties while at the same time allowing contact with theanalytes (e.g., polyhydroxyl compounds, H⁺ and OH⁻), and binding of thepolyhydroxyl compounds to the boronic acid. Therefore, the matrix isinsoluble in the medium and in close association with it by establishinga high surface area interface between matrix and analyte solution. Thematrix also does not interfere with transport of the analyte to thebinding sites so that equilibrium can be established between the twophases. In one embodiment, an ultra-thin film or microporous supportmatrix may be used. In another embodiment, the matrix that is swellablein the analyte solution (e.g. a hydrogel matrix) can be used for aqueoussystems. In some embodiments, the sensing polymers are bonded to asurface such as the surface of a light conduit, or impregnated in amicroporous membrane. Techniques for preparing ultra-thin films,microporous polymers, microporous sol-gels, and hydrogels have beenestablished in the prior art.

In one preferred embodiment, the boronic acid substituted viologen maybe covalently bonded to a fluorescent dye. The adduct may be apolymerizable compound or a unit in a polymer. One such adduct forexample may be prepared by first forming an unsymmetrical viologen from4,4′-dipyridyl by attaching a benzyl-3-boronic acid group to onenitrogen and an aminoethyl group to the other nitrogen atom. Theviologen is condensed sequentially first with8-acetoxy-pyrene-1,3,6-trisulfonyl chloride in a 1:1 mole ratio followedby reaction with excess PEG diamine to obtain a prepolymer mixture. Anacid acceptor is included in both steps to scavenge the byproduct acid.The prepolymer mixture is crosslinked by reaction with a polyisocyanateto obtain a hydrogel. The product is treated with base to remove theacetoxy blocking group. Incomplete reaction products and unreactedstarting materials are leached out of the hydrogel by exhaustiveextraction with deionized water before further use. The product isresponsive to glucose when used as the sensing component as describedherein.

Alternatively, such adducts are ethylenically unsaturated monomerderivatives. For example, dimethyl bis-bromomethyl benzene boronate isreacted with excess 4,4′-dipyridyl to form a half viologen adduct. Afterremoving the excess dipyridyl, the adduct is further reacted with anexcess of bromoethylamine hydrochloride to form the bis-viologen adduct.This adduct is coupled to a pyranine dye by reaction with the8-acetoxypyrene-tris sulfonyl chloride in a 1:1 mole ratio in thepresence of an acid acceptor followed by reaction with excessaminopropylmethacrylamide. Finally, any residual amino groups may bereacted with methacrylol chloride. After purification, the dye/viologenmonomer may be copolymerized with HEMA and PEGDMA to obtain a hydrogel.

SOLUTION EXAMPLE

To a solution of HPTS-CysMA (1×10⁻⁵ M in pH 7.4 PBS) was addedincreasing amounts of 3,3′-oBBV (30 mM in MeOH) and the fluorescenceemission measured after each addition. FIG. 15 gives the relativeemission change (Stern-Volmer curve) upon addition of 3,3′-oBBV (Q)indicating the quenching of HPTS-CysMA with 3,3′-oBBV. The fluorimetersettings were as follows: 1% attenuation, ex slit 8 nm, em slit 12 nm,486 nm ex λ, 537 nm em λ.

HPTS-CysMA (1×10⁻⁵ M) and 3,3′-oBBV (3×10⁻³ M) were titrated with astock solution of glucose (31250 mg/dL) in pH 7.4 PBS and thefluorescence emission measured after each addition of glucose. Therelative change upon addition of glucose is given in FIG. 16.

HYDROGEL EXAMPLE

HPTS-CysMA (2 mg), 3,3′-oBBV (15 mg), N,N′-dimethylacrylamide (400 mg),N,N′-methylenebisacrylamide (8 mg), HCl (10 μL of 1 M solution), andVA-044 (1 mg) were dissolved in water and diluted to 1 mL in avolumetric flask. The solution was freeze-pump-thawed (3×), injectedinto a mold containing a 0.005″ polyimide spacer and polymerized at 55°C. for 16 h. The resultant film was placed in pH 7.4 phosphate bufferand was tested in a flow cell configuration with increasing amounts ofglucose (0, 50, 100, 200, 400 mg/dL). The relative fluorescence changeupon addition of glucose is given in FIG. 17. The fluorimeter settingswere as follows: ex slit 8 nm, em slit 3.5 nm, 515 nm cutoff filter, 486nm ex λ, 532 nm em λ.

Although the foregoing invention has been described in terms of certainembodiments and examples, other embodiments will be apparent to those ofordinary skill in the art from the disclosure herein. Moreover, thedescribed embodiments have been presented by way of example only, andare not intended to limit the scope of the inventions. Indeed, the novelmethods and systems described herein may be embodied in a variety ofother forms without departing from the spirit thereof. Accordingly,other combinations, omissions, substitutions and modifications will beapparent to the skilled artisan in view of the disclosure herein. Thus,the present invention is not intended to be limited by the example orpreferred embodiments. The accompanying claims provide exemplary claimsand their equivalents are intended to cover forms or modifications aswould fall within the scope and spirit of the inventions.

What is claimed is:
 1. A sensor for detecting an analyte concentrationin a blood vessel, comprising: an optical fiber with proximal and distalends; an atraumatic tip portion with proximal and distal ends, whereinthe proximal end of the atraumatic tip portion is separated from thedistal end of the optical fiber, such that a gap exists between theatraumatic tip portion and the optical fiber; a rod with proximal anddistal ends, wherein the proximal end of the rod is attached to thedistal end of the optical fiber, and wherein the distal end of the rodis attached to the proximal end of the atraumatic tip portion, such thatthe rod traverses the gap and couples the optical fiber to theatraumatic tip portion; a chemical indicator system disposed within thegap and capable of generating an emission light signal in response to anexcitation light signal, wherein the intensity of the emission lightsignal is related to the analyte concentration; and a selectivelypermeable membrane disposed over the gap, wherein the sensor is sizedfor deployment within the blood vessel.
 2. The sensor of claim 1,wherein the chemical indicator system is further immobilized within thegap by a hydrogel.
 3. The sensor of claim 1, further comprising atemperature sensor.
 4. The sensor of claim 1, wherein the optical fiberhas a diameter of between about 0.005 inches and about 0.020 inches. 5.The sensor of claim 1, further comprising a reflective region.
 6. Thesensor of claim 5, wherein the reflective region comprises a reflectivesurface of the proximal end of the rod.
 7. The sensor of claim 1,wherein the rod is attached to the optical fiber by heating.
 8. Thesensor of claim 1, wherein the rod is attached to the optical fiber by areflective adhesive.
 9. The sensor of claim 8, wherein the shape of thedistal end of the atraumatic tip portion is configured to reduce traumawithin the blood vessel and selected from the group consisting ofhemispherical, parabolic, and elliptical.
 10. The sensor of claim 1,wherein the distal end of the atraumatic tip portion is flexible. 11.The sensor of claim 1, wherein the distal end of the atraumatic tipportion is deformable.
 12. The sensor of claim 1, wherein the distal endof the atraumatic tip portion is formed from at least one materialselected from the group consisting of plastics, polymers, gels, metalsand composites.
 13. The sensor of claim 1, wherein the rod is formedfrom at least one material selected from the group consisting of metal,metal alloy, plastic, polymer, ceramic, and composite material.
 14. Thesensor of claim 13, wherein the rod is formed from stainless steel,titanium, or Nitinol.
 15. The sensor of claim 1, wherein the rod iscylindrical.
 16. The sensor of claim 15, wherein the rod diameter isbetween about 0.002 inches and about 0.010 inches.
 17. The sensor ofclaim 1, wherein the rod is flexible.
 18. The sensor of claim 1, whereinthe rod is stiffer than the optical fiber.
 19. The sensor of claim 1,wherein the rod is sufficiently stiff to prevent flexing of the sensoralong the gap.
 20. A sensor for detecting an analyte concentration in ablood vessel, comprising: an optical fiber with proximal and distalends; an atraumatic tip portion with proximal and distal ends, whereinthe proximal end of the atraumatic tip portion is separated from thedistal end of the optical fiber, such that a gap exists between theatraumatic tip portion and the optical fiber; a hypotube with proximaland distal ends, wherein the proximal end of the hypotube is attached tothe distal end of the optical fiber, and wherein the distal end of thehypotube is attached to the proximal end of the atraumatic tip portion,such that the hypotube traverses the gap and couples the optical fiberto the atraumatic tip portion, wherein the hypotube comprises at leastone window that opens onto the gap; a chemical indicator system disposedwithin the gap and capable of generating an emission light signal inresponse to an excitation light signal, wherein the intensity of theemission light signal is related to the analyte concentration; and aselectively permeable membrane disposed over the at least one window,wherein the sensor is sized for deployment within the blood vessel. 21.The sensor of claim 20, wherein the chemical indicator system is furtherimmobilized within the gap by a hydrogel.
 22. A sensor for detecting ananalyte concentration in a blood vessel, comprising: an optical fiberwith proximal and distal ends; an atraumatic tip portion with proximaland distal ends, wherein the proximal end of the atraumatic tip portionis separated from the distal end of the optical fiber, such that a gapexists between the atraumatic tip portion and the optical fiber; a cageconnecting the optical fiber and atraumatic tip portion, wherein theoptical fiber is at least partially enclosed within the cage, andwherein the cage has at least one window; a chemical indicator systemdisposed within the cage, wherein the chemical indicator system isadjacent the window and is separated from analyte by a selectivelypermeable membrane, and wherein the chemical indicator system is capableof generating an emission light signal in response to an excitationlight signal, wherein the intensity of the emission light signal isrelated to the analyte concentration; and a reference material, whereinthe reference material is configured to either reflect a portion of theexcitation light signal before the excitation light signal enters thechemical indicator system or to return a second emission light signal,wherein the intensity of the second emission light signal is not relatedto the analyte concentration.
 23. A sensor for detecting an analyteconcentration in a blood vessel, comprising: an optical fiber with aproximal end and a distal end, wherein the distal end of the opticalfiber comprises a glucose sensing hydrogel and wherein the glucosesensing hydrogel comprises a first fluorophore, a quencher, and at leastone glucose binding moiety; a reference fiber adjacent the optical fiberhaving a proximal end and a distal end, wherein the distal end of thereference fiber comprises a reference material, wherein the referencematerial comprises a second fluorophore; a light emitting diode operablycoupled to the glucose fiber and the reference fiber, wherein the lightemitting diode sends an excitation light to the glucose fiber and thereference fiber; a glucose signal detector operatively coupled to theglucose fiber, wherein the glucose signal detector receives a firstfluorescent light from the glucose fiber; and a reference signaldetector operatively coupled to the reference fiber, wherein thereference signal detector receives a second fluorescent light from thereference fiber.
 24. The sensor of claim 23, wherein the firstfluorophore is the same as the second fluorophore.
 25. The sensor ofclaim 23, wherein the first fluorophore is different than the secondfluorophore.
 26. The sensor of claim 23, wherein the reference materialcomprises a quencher.
 27. The sensor of claim 23, wherein the referencematerial is encased in a glucose impermeable membrane.